Sound output device and attachment aid member

A sound output device includes a device main frame in which at least a speaker is disposed, and an attachment aid member that is joined to the device main frame. In the sound output device, the attachment aid member includes an annular support portion at least a part of which is inserted into a cavum concha, and the annular support portion includes a contact portion that comes into contact with a part of an ear in the cavum concha while being elastically deformed. With this arrangement, the contact portion of the annular support portion inserted into the cavum concha comes into contact with a part of the ear in the cavum concha while being elastically deformed. Accordingly, it is possible to attach the sound output device to the ear, using the attachment aid member, regardless of the size and the shape of the ear.